This application includes a computer program listing appendix, submitted on compact disc (CD). The content of the CD is hereby incorporated by reference in its entirety and accordingly forms a part of this specification. The CD contains the following file:
File name: Angle.txt
File size: 38.1 kb
Creation date for CD: Nov. 21, 2002
1. Field of the Invention
The present invention relates generally to the fields of position sensors and the analysis of positional data. More particularly, it concerns methods and apparatuses for efficiently reconstructing angle information by analyzing data from a set of independent sensors. Even more particularly, it. concerns the reconstruction of angle information by comparing a data set from independent sensors with a calibration data set and minimizing an error function between those sets of data to reconstruct angle information.
2. Description of Related Art
The ability to gather data from one or more sensors and translate that data into meaningful positional information is important in a wide variety of disciplines. For instance, tracking objects is essential for commercial aircraft controllers and an assortment of military applications.
Over the years, sundry techniques aimed at determining positional information, such as angular information, from sensor readings have been developed. Although each has shown at least a degree of success in its respective application, room for significant improvement remains.
U.S. Pat. No. 5,724,047, which is hereby incorporated by reference, involves a precision direction finding system for making precision angle of arrival estimates for a signal received through two antenna elements separated in space. Phase interferometry is used to determine a precise angle of arrival, with multiple ambiguities due to the periodic nature of the phase difference related to geometric angle. The interferometric ambiguities are resolved using the time difference of arrival (TDOA) of the signal at the two antenna elements. TDOA is measured using leading edge envelope detection for simple pulsed signals, and predetection correlation for phase and frequency modulated signals. Although such phase interferometry determinations may exhibit certain advantages over other conventional methods, shortcomings remain due to, at least in part, the relatively complex nature of the computations required to implement the methodology. Further, reliance upon two antenna elements, rather than a plurality of independent sensors, may inhibit at least some flexibility of such a system.
U.S. Pat. No. 6,104,345, which is hereby incorporated by reference, involves a method for the direction of arrival (DOA) tracking of at least one source, along a single azimuth axis or along both azimuth and elevation axes. The method includes the steps of selecting all the high peaks from a DOA function as potential track points, converting the potential track points into a plurality of tracks and selecting a true track from the plurality of tracks. This methodology also suffers from some shortcomings; for example, it may be desirable to avoid the particular computational complexity involved with selecting a true track from the plurality of potential track points.
U.S. Pat. No. 4,562,439, which is hereby incorporated by reference, involves an imaging radar seeker for producing two-dimensional images of a target, which can be mounted on a missile or other moving body, such as an automobile. A computer directs the seeker to operate sequentially in searching, tracking, and imaging modes. In the searching mode, a combination of circumferential rotation of an antenna of the seeker and frequency scanning of electromagnetic energy fed to the antenna enables the seeker to search for its target over a conical field-of-view or a wider, peripheral belt field-of-view. In the imaging mode, circumferential rotation of an antenna is stopped, and the tilt angle of a linear array of the antenna is stepped or continuously moved to compensate for radial movement of a radiated beam caused by frequency stepping imparted by a frequency synthesizer. This keeps the beam fixed in space and centered on the target. Inverse synthetic aperture imaging is used to create a two-dimensional image of the target wherein the first dimension (range) is obtained by performing inverse Fourier transforms on the echo signals, and the second orthogonal dimension (cross-range or doppler frequency) is obtained by performing Fourier transforms. The array can be a linear array of E-plane stacked linear waveguide antenna elements operating in either the traveling wave mode or the standing wave mode. Such methodology too exhibits shortcomings at least due to its complexity, lack of flexibility, and its inability to more efficiently perform angle reconstruction determinations.
U.S. Pat. No. 5,818,393, which is hereby incorporated by reference, involves a fixed body wide field-of-view conformal antenna array suitable for broadband precision direction finding on missile platforms. The array is configured as multiple sub-arrays of spiral antennas that cover particular regions within the desired field-of-view of the entire array. A lower cost, more reliable and more accurate direction finding solution for missile needs is provided, primarily by the elimination of conventional radomes and antenna gimbal structures. The array can be configured to include multi-mode sensors. Although useful in this elimination of structures, this methodology exhibits room for significant improvement given its inability to more efficiently reconstruct angular information.
U.S. Pat. No. 6,313,794, which is hereby incorporated by reference, uses feedback from RF carrier frequency measurements to disassociate the emitter angle-of-arrival component in the ambiguous phase measurement from the initially unknown phase measurement integer ambiguities. It then resolves the ambiguities and obtains the correct emitter angle-of-arrival (AOA). This is accomplished by converting the actual interferometer baselines on which the unassociated pulse phase measurements were made at different emitter frequencies to a baseline set for a single-frequency equivalent interferometer array. This methodology, as with the methodologies described above, suffers from issues relating to complexity, flexibility, and the inability to more quickly and efficiently reconstruct high-resolution angular information.
U.S. Pat. No. 5,657,251, which is hereby incorporated by reference, involves a computer-implemented process for processing incoming target data from a focal plane or scanning radar to accomplish multiple Target Tracking. Inputs are pixel plane coordinates and intensity of target blips. The Intelligent Target Tracking Processor (ITTP) employs an optimal target tracking algorithm. An optimal observation-to-track assignment exists when all target blips in a new frame of target data are matched up with nearby tracks, such that the sum of all the distances from each target blip to its assigned track is minimized. An expert system is used to control overall processing flow and provide efficient allocation of computing resources. Target blips without near neighbors are allowed to go directly to a real track table of established tracks, if their coordinates match-up with projected tracking gates. Otherwise, target blips are tested sequentially against two-frame, three-frame, and four- or higher-frame discriminants, to reject blips not belonging to established tracks. The ITTP can partition the pixel plane into xe2x80x9cbite size partitionsxe2x80x9d, each with a manageable number of target blips, which it handles sequentially. The ITTP is designed to handle hundreds or thousands of targets as a stand-alone processor as is required in space object tracking or military scenarios. The expert system maintains an optimum balance between correlating on existing tracks and discriminating against impossible tracks. A total of 26 different metric and radiometric target tracking discriminants are employed. The ITTP is a dynamically and optimally configured set of general purpose parallel processors. Although useful for trajectory tracking for applications such as air-traffic controlling, this methodology nevertheless includes shortcomings; for instance, it does not allow for the reconstruction of high quality, high resolution angle information using a plurality of independent sensors or detectors on an image plane.
Problems enumerated above are not intended to be exhaustive, but rather are among many that tend to impair the effectiveness of previously known techniques concerning positional tracking and the determination of angle information. Other noteworthy problems may also exist; however, those presented above should be sufficient to demonstrate that methodology appearing in the art have not been altogether satisfactory. In particular, existing techniques do not adequately allow for the determination of angle information with improved resolution from independent sensors or detectors on an image plane.
Shortcomings listed above are reduced or eliminated by the techniques disclosed herein. These techniques are applicable to a vast number of applications, including general targeting and tracking applications.
In one respect, the invention is a method for determining angular information from a target. Measured amplitude data is obtained from a plurality of sensors. An azimuth and elevation are estimated using the measured amplitude data. Calibrated amplitude data corresponding to the azimuth and elevation is obtained. A residual error between the measured amplitude data and the calibrated amplitude data is determined. Aspects of this process are performed iteratively until the residual error is minimized. The angular information, which corresponds to the azimuth and elevation at which the residual error was minimized, is then output.
In other respects, the invention is a computer program, comprising computer or machine readable program elements translatable for implementing the method described above. Further the invention is an apparatus for performing such a method.
In another respect, the invention is a method for determining angular information from a target. A plurality of sensors on an image plane are obtained. The target or a point target is defocused on the image plane such that one or more of the sensors respond to a target pulse. Measured amplitude data from the plurality of sensors is obtained. An azimuth and elevation are estimated using the measured amplitude data. Calibrated amplitude data corresponding to the azimuth and elevation is obtained. A residual error between the measured amplitude data and the calibrated amplitude data is determined. Aspects of this process are performed iteratively until the residual error is minimized. The angular information, which corresponds to the azimuth and elevation at which the residual error was minimized, is then output.
In other respects, the invention is a computer program, comprising computer or machine readable program elements translatable for implementing the method described above. Further the invention is an apparatus for performing such a method.
In another respect, the invention is a system for determining angular information from a target. The system includes a plurality of sensors and a computer. The computer is configured to: (a) acquire measured amplitude data from the plurality of sensors; (b) estimate an azimuth and elevation using the measured amplitude data; (c) access calibrated amplitude data corresponding to the azimuth and elevation; (d) determine a residual error between the measured amplitude data and the calibrated amplitude data; and (e) output the angular information as corresponding to the azimuth and elevation at which the residual error is minimized.